1. Field of the Invention
The present invention relates to a method of cutting out a cut sheet having constant dimensions from a weak sheet, and more particularly, it relates to a method of cutting out a cut sheet from a ceramic green sheet which is to be employed for making a laminated ceramic capacitor, for example.
2. Description of the Background Art
In general, a laminated ceramic capacitor comprises a plurality of stacked ceramic sheets, a plurality of internal electrodes which are opposed to each other on opposite sides of the respective ceramic sheets and a pair of external electrodes provided on a pair of opposite end surfaces of the laminate formed by the plurality of ceramic sheets. The plurality of internal electrodes are electrically connected to respective ones of the external electrodes in an alternate manner.
A conventional laminated ceramic capacitor has been generally manufactured in the following manner: A ceramic material in the form of slurry is applied onto a carrier film (base film) of polyester, for example, by a coating method, such as a doctor blade method in uniform thickness. Then the ceramic material provided on the carrier film is dried. Thus, a ceramic green sheet is formed on the carrier film. Then, an internal electrode is printed on the surface of the ceramic green sheet by screen printing. Then the internal electrode, the carrier film and the ceramic green sheet are passed through a drying furnace to be dried. Thereafter the ceramic green sheet 3 is separated from the carrier film 1 by a suction roller 2, as shown in FIG. 4. The separated ceramic green sheet 3 is placed on an endless belt 4, which is partially shown in FIG. 4, and carried along as indicated by arrow 5, to be then positioned on a surface plate 6. The belt 4 is formed by a thin plate of a metal such as nickel, and provided with a large number of pores 7, as shown in FIG. 5. The surface plate 6 is provided with a plurality of suction holes 8. Negative pressure is applied to the suction holes 8 to draw the ceramic green sheet 3 downward by suction provided through the pores 7, thereby to locate the ceramic green sheet 3 securely on the surface plate 6.
As shown in FIG. 4, a vertically movable pickup apparatus 10 is positioned above the ceramic green sheet 3. The pickup apparatus 10 has a punching edge 11 at its periphery and is provided with a suction head 12 in a portion thereof enclosed by the punching edge 11. The suction head 12 is provided with a plurality of suction holes 13.
When the pickup apparatus 10 is downwardly moved as shown in FIG. 5, the punching edge 11 defines a cutting line having a closed outline, that is, a continuous cut, in the ceramic green sheet 3. Then the pickup apparatus 10 is upwardly moved so that a cut sheet 3a, which is in contact with the lower surface of the suction head 12 and enclosed by the aforementioned cutting line, is taken out from the remaining part of the ceramic green sheet 3.
Thereafter a prescribed number of such cut sheets 3a are stacked and then pressure is applied thereto. A laminate of the sheet cuts 3a thus obtained is cut in dimensions for providing an individual capacitor, if necessary. Then this laminate is fired. Silver paste members are applied to opposite end surfaces of the fired laminate and then baked, thereby to form a pair of external electrodes. A desired ceramic laminated capacitor is obtained in such a manner.
Alternatively, the internal electrode may be alternatively printed after the cut sheet 3a is obtained, by performing cutting as shown in FIG. 4.
In the aforementioned method, the ceramic green sheet 3 is necessarily independently suspended as it is transferred to the belt 4 after being separated from the carrier film 1. That is, the ceramic green sheet 3 is in an unsupported, independent state on both the upstream and downstream sides of the suction roller 2 in the example shown in FIG. 4. As a result, the ceramic green sheet 3 may be deformed, broken or wrinkled if the same is thin, i.e., mechanically weak. Thereafter, it is difficult to obtain the cut sheet 3a with high dimensional accuracy, and hence the production yield of laminated ceramic capacitors is reduced as the result.
Further, this method requires great accuracy of the straightness of the punching edge 11, which is directly brought into contact with the surface of the belt 4 of nickel or the like in order to cut the ceramic green sheet 3. If the punching edge 11 is inferior in straightness, it is not possible to completely cut through the ceramic green sheet 3. Further, the life of the punching edge 11 is reduced since the same is brought into contact with the hard belt 4 when cutting the ceramic green sheet 3 is cut. If the punching edge 11 is chipped, metal scraps may be mixed into the ceramic green sheet 3.